With reference to FIG. 3, a known transmission case is disclosed, which includes an assembling hole portion H and a snap ring S preassembled hereto. When fixing a bearing (not shown) to the case C, a first distance between both ends E of the snap ring S can be expanded within the assembling hole H. The bearing is used for supporting a rotational shaft K. The assembling hole portion H comprises a single large-aperture hole portion.
Because the single hole portion which is comprising the assembling hole portion H that is provided to the case, the assembling hole portion requires a widely-opened aperture at a position where the both ends E of the snap ring S are located, in order to expand the both ends E of the snap ring S. Because interference of the both ends when they are being expanded needs to be prevented, the diameter of the assembling hole portion is needed to be large.
In order to have a large-aperture assembling hole portion H, a large space needs to be secured. However, having a large assembling hole portion causes degradation in case rigidity so that the case needs to be reinforced.
More specifically, when fixing the bearing to the case C, a tool to expand the snap ring S is essential. Because a single assembling hole portion H is constructed to the case C, the aperture of the assembling hole portion becomes large. Problems thus exist for a large-aperture hole portion, that are, the case C needs to be reinforced due to degradation in rigidity and large space is needed for the large-aperture hole portion.
Considering the above conventional problems, the inventors of the application have focused on dividing the assembling hole portion into two for fixing the bearing to the case.
Further, according to the aforementioned idea, the dual hole portions are located where the both ends of the snap ring are located, so that the both ends of the snap ring can be expanded within the dual hole portions. The case includes an assembling hole portion and a snap ring preassembled hereto. When fixing a bearing to the case, a first distance between both ends of the snap ring can be expanded within the assembling hole portion. The bearing is used for supporting a rotational shaft. Consequently, saving space and maintaining the case rigidity can be achieved.